SPOTTED WING DROSOPHILA ALERT: AUGUST 10, 2018

Captures of spotted wing drosophila (SWD) fruit flies in vinegar/yeast traps in raspberry and highbush blueberry plantings are now increasing in most locations, and at most sites counts rose above threshold levels, including one site with over 200 flies caught. (See table below.) The wet weather predicted for next week may further encourage SWD infestations, as these insects like moisture, and the rain will also lead to more rotten fruit in the field. Most summer-bearing raspberry fields are through or nearly through harvest, but fall fruiting raspberries and blackberries are now ripening and are very susceptible to infestation. Later ripening blueberries and elderberries are also good hosts for SWD at this time. Growers with these crops should be putting on protective sprays. Pay close attention to product pre-harvest intervals and limits on the number of applications allowed for each product, to develop a management strategy that will be most effective for your situation.

Where brand names or company names are used it is for the reader’s information. No endorsement is implied nor is any discrimination intended against other products with similar ingredients. Always consult product labels for rates, application instructions and safety precautions. Users of these products assume all associated risks.

The University of Maine is an equal opportunity/affirmative action institution.

CORN EARWORM, FALL ARMYWORM THREAT INCREASES

Silking Corn Fields Require Protection

SITUATIONAll but the latest planted fields are now silk or beyond. Storm fronts approaching from the south and west have brought up more corn earworm and some fall armyworm to threaten fields with silking corn. Fall armyworm can be troubling at this time, as eggs laid on silking corn allow larvae to move into the ears undetected by field scouting.

European corn borer: Moth activity declined in most locations this week, with the exception of a site in Sabattus. The five moths/week threshold was only exceeded in Sabattus and one Wells site. However, both of these sites were also under a spray interval for corn earworm, which should also protect against corn borer. Feeding damage was very light, with no sites over the 15% spray threshold for pre-tassel to silking corn.

Corn earworm: Numbers of moths caught in traps increased at many sites this week, leading to sprays recommended for nearly all silking fields. A 6-day spray interval for all silking corn was recommended for one site in Wells. A 5-day spray interval was recommended for Bowdoinham, Charleston, one Lewiston site, Palmyra, Sabattus and Wayne. A 4-day spray interval was recommended for silking fields in Biddeford, Cape Elizabeth, Dayton, Levant, and one Wells site.

Corn Earworm Larvae, photo by David Handley

Fall Armyworm on Corn Silk, photo by David Handley

Fall armyworm: We have started catching moths in our pheromone traps this week, but these have not yet been widespread. This species has historically been the most challenging to trap, and in some years the traps have performed poorly in terms of predicting the damage we find in the field and ears. This may be the situation this season as we have heard from a grower of ears being infested, despite no captures of moths in our traps. This is why we recommend growers consider applying an insecticide when the corn is in the late pre-tassel to tassel/early silk stage, especially if any moth activity or feeding damage has been observed in the field, because this is often when caterpillars are most exposed, as they move from one part of the plant to another. It is also the time when protection of the emerging silk is most critical to prevent infestation. Furthermore, fall armyworm larvae can be difficult to control despite regular sprays, as they tend to be more resistant to many of the insecticides used in corn than the other species we target. Remember, the larvae also tend to be more exposed at night, making evening sprays more effective. The addition of a spreader-sticker with the insecticide can also help to get the best coverage possible and extend the effective time of the application.

Corn leaf aphids: These insects often infest corn plants later in the season, especially in fields that have not recently been sprayed for other pests. Colonies of bluish-green aphid can cover tassels, stalks and husks. Their waste encourages the dark, slimy sooty mold fungus, which covers the surface of the husks. Sprays for corn earworm will usually control aphids.

Aphids on Corn Tassel, photo by Kaytlin Woodman

Rust on Corn, photo by David Handley

Corn rust: Rust is a fungus disease that causes reddish-brown pustules on corn leaves and husks, reducing the quality of the ears. A fungicide spray for rust would only be recommended if the infection were noticed in a field prior to tasseling. Later infections are unlikely to cause enough damage to the crop to justify control measures. Materials available to control corn rust include Quadris®, Bravo®, and Quilt®.

Thresholds apply only to corn with exposed fresh silk. Lengthen spray intervals by one day if maximum daily temperature is less than 80°F.

European Corn Borer ThresholdsWhorl stage: 30% or more of plants scouted show injury.Pre-tassel-silk: 15% or more of plants scouted show injury.Silk: 5 or more moths caught in pheromone traps in one week.

Where brand names or company names are used, it is for the reader’s information. No endorsement is implied nor is any discrimination intended against other products with similar ingredients. Always consult product labels for rates, application instructions and safety precautions. Users of these products assume all associated risks.

The University of Maine is an equal opportunity/affirmative action institution.

Captures of spotted wing drosophila (SWD) fruit flies in vinegar/yeast traps in raspberry and highbush blueberry plantings remained low in most locations, although at two sites ((Limington, Readfield) counts rose above threshold levels. (See table below.) The recent warm, wet weather will encourage SWD infestations, however, as it may lead to more rotten fruit in the field and increase ambient moisture levels. Growers should try to keep rotten fruit out of the field as much as possible and encourage dry conditions by pruning out excess growth, especially near the base of the plantings. Growers who have been catching flies in their traps for more than one week and have ripening fruit should put on a protectant spray.

We expect spotted wing drosophila populations to increase significantly in the coming weeks as more ripe and rotten fruit becomes available for the flies. Protective sprays should be applied if more than four spotted wing drosophila flies are caught in a trap, flies are caught consistently for more than one week, or any larvae are noticed in the fruit. Look for fruit flies hovering around fruit and symptoms of premature fruit decay.

For more information on identifying spotted wing drosophila and updates on populations around the state, visit our SWD blog.

Where brand names or company names are used it is for the reader’s information. No endorsement is implied nor is any discrimination intended against other products with similar ingredients. Always consult product labels for rates, application instructions and safety precautions. Users of these products assume all associated risks.

The University of Maine is an equal opportunity/affirmative action institution.

CORN EARWORM THREATENS ALL SILKING CORN

Most Sites Now Have Significant Moth Populations in Silking Corn

SITUATIONAs predicted, the warm weather from the south has brought an increase in insect activity, as we come into the peak of the sweet corn season. Growers should be monitoring their fields regularly and be prepared to protect silking corn from the threat of earworm and corn borer. Fall armyworm is likely to become more of a threat in the coming days.

European corn borer: Activity in pheromone traps increased in most fields this week, although it has not yet led to a noticeable increase in feeding damage. This will likely follow soon however, as the eggs these moths are laying begin to hatch. When more than 5 moths are caught in a trap in a week, a spray is recommended for all silking corn to prevent larvae from entering the ears directly after hatching. Moths exceeded this threshold in Bowdoinham, Garland, Lewiston, New Gloucester, Oxford and Wells. However, all of these sites, except the one Wells field, were also under a spray interval for corn earworm, which should also protect against corn borer. Feeding damage in the field was very light, with no sites over the 15% spray threshold for pre-tassel to silking corn; but this is likely to increase soon.

European Corn Borer Larva, photo by David Handley

Corn Earworm Feeding on Corn, photo by David Handley

Corn earworm: Numbers of moths caught in traps increased significantly at nearly all sites monitored this week, leading to sprays recommended for corn in most silking fields. A 6-day spray interval for all silking corn was recommended for our sites in Bowdoinham, one Lewiston site, North Berwick, and Oxford. A 5-day spray interval was recommended for one Cape Elizabeth site, Dayton, Garland, one Lewiston site, Nobleboro, Poland, Sabattus and Wayne. A 4-day spray interval was recommended for silking fields in Biddeford, one Cape Elizabeth site, one Dayton site, Levant, New Gloucester, and one Wells site. At this point, it is likely corn earworm pressure will continue and growers should be prepared to protect all silking corn.

Fall armyworm: No moths were caught in our pheromone traps this week, but we anticipate we will be seeing them soon because we are finding some larval feeding. None of the injury was over the 15% spray threshold.

Squash vine borer: Moths were over the 5 moth per week threshold in Oxford. All other sites had either one or no moths this week.

Spotted wing drosophila: Fly counts have been variable this week, with some locations seeing increases (Limington, Readfield) while most locations still had very few, if any flies. The recent heat and rain will improve conditions for spotted wing drosophila (SWD), because they likely increased the amount of rotten fruit in the field and the level of moisture. Both are conducive to fly presence and reproduction. Try keep the planting as free from rotten fruit as possible, remove excess vegetative growth, especially near the base of the plants, and apply a suitable insecticide when flies are observed or larvae are found in the fruit. For more information visit our SWD blog.

Thresholds apply only to corn with exposed fresh silk. Lengthen spray intervals by one day if maximum daily temperature is less than 80°F.

European Corn Borer ThresholdsWhorl stage: 30% or more of plants scouted show injury.Pre-tassel-silk: 15% or more of plants scouted show injury.Silk: 5 or more moths caught in pheromone traps in one week.

Where brand names or company names are used, it is for the reader’s information. No endorsement is implied nor is any discrimination intended against other products with similar ingredients. Always consult product labels for rates, application instructions and safety precautions. Users of these products assume all associated risks.

The University of Maine is an equal opportunity/affirmative action institution.

SPOTTED WING DROSOPHILA ALERT: JULY 27, 2018

We continue to capture spotted wing drosophila fruit flies in vinegar/yeast traps in raspberry and highbush blueberry plantings this week, but mostly in low numbers. (See table below.) While these counts may indicate that populations are still fairly low in berry fields, growers who have been catching flies in their traps for more than one week and have ripening fruit should put on a protectant spray. We have had reports of raspberry fruit infested with larvae from an unsprayed field.

Spotted wing drosophila populations are expected to rise in the coming weeks as more ripe fruit becomes available for the flies, especially if conditions remain warm and wet. Set out traps now, if you haven’t already. Start protective sprays on any berries that have begun to ripen when: more than four spotted wing drosophila flies are caught in a trap, flies are caught consistently for more than one week, or any larvae are noticed in the fruit. Look for fruit flies hovering around fruit and symptoms of premature fruit decay.

Remember to keep waste fruit out of the field as much as possible. Harvest often and regularly to prevent the presence of overripe fruit; and open up the planting to more light by pruning out excess vegetative growth, especially in the lower part of the bush canopy.

For more information on identifying spotted wing drosophila (SWD) and updates on populations around the state, visit our SWD blog.

Where brand names or company names are used it is for the reader’s information. No endorsement is implied nor is any discrimination intended against other products with similar ingredients. Always consult product labels for rates, application instructions and safety precautions. Users of these products assume all associated risks.

The University of Maine is an equal opportunity/affirmative action institution.

CORN EARWORM NUMBERS CLIMBING

Populations Spotty, but Some Fields Severely Threatened

SITUATIONCorn harvest is coming into full swing for early varieties in southern and mid-coast farms. Warm weather has pushed maturity of later varieties, so we may see some concentration of maturity in the coming days. Warm air and rain coming up from the south over the past week has brought some corn earworm into the state, but not yet to the levels we expected. The warm air flow continues, however; so it is likely that pest pressure will increase in the coming days.

European Corn Borer in Tassel, photo by David Handley

European corn borer: Activity in both pheromone traps and the fields remained very low this week. We did find pupae in stalks, which may indicate that we could see a second generation of corn borer this year that might threaten late corn. Moths were caught in Biddeford, Cape Elizabeth, Dayton, Lewiston, North Berwick, Oxford, and Wales. They were below threshold for silking corn at all of these sites. Feeding damage in the field was very light, with no sites over the 15% spray threshold for pre-tassel to silking corn.

Corn earworm: Numbers of moths caught in traps this week were quite variable and didn’t seem to follow any geographic pattern. A 6-day spray interval for all silking corn was recommended for our sites in Biddeford, Cape Elizabeth and Sabattus. A 5-day spray interval was recommended for Bowdoinham and Garland. A 4-day spray interval was recommended for a silking field in Levant. As the weather for the coming week is predicted to continue coming up from the south, we should expect corn earworm pressure to continue and be prepared to protect all silking corn.

Fall armyworm: No moths were caught in our pheromone traps this week, but we have found some larval feeding damage in the cornfields we’ve scouted. This is not unusual; our traps often don’t catch the first moths into the fields, so we see feeding injury before we see moths. No feeding injury was over the 15% spray threshold. We also continue to see a small amount of feeding injury from common army worm, but we expect these larvae to be pupating very soon. The anticipated weather pattern could bring a rapid increase in fall armyworm numbers in the coming days.

Squash vine borer moths were caught in pheromone traps in Biddeford, Lewiston, Wells and Oxford. Only the Oxford site, which had 5 moths, was over the spray threshold. All other sites were below the spray threshold, Counts may still increase in the coming days, so growers should continue scouting for vine borer symptoms and protect squash plants if moths or damage are seen. See the 2018-2019New England Vegetable Management Guide for control options.

Spotted wing drosophila: We continue to capture spotted wing drosophila (SWD) flies around the state, but still in relatively low numbers. We have had reports of larval infestation of unsprayed raspberry fruit, so growers who have been capturing flies in traps for more than one week should protect ripening fruit, if sprays have not yet been applied. For more information visit our SWD blog.

Thresholds apply only to corn with exposed fresh silk. Lengthen spray intervals by one day if maximum daily temperature is less than 80°F.

European Corn Borer ThresholdsWhorl stage: 30% or more of plants scouted show injury.Pre-tassel-silk: 15% or more of plants scouted show injury.Silk: 5 or more moths caught in pheromone traps in one week.

Where brand names or company names are used, it is for the reader’s information. No endorsement is implied nor is any discrimination intended against other products with similar ingredients. Always consult product labels for rates, application instructions and safety precautions. Users of these products assume all associated risks.

The University of Maine is an equal opportunity/affirmative action institution.

SPOTTED WING DROSOPHILA ALERT: JULY 20, 2018

We have found spotted wing drosophila (SWD) fruit flies in raspberry and highbush blueberry plantings in Maine over the past week, in most of the locations where we have set up traps. (See table below.) This compliments reports from throughout the northeast that SWD is active and in high numbers very early this season.

Some of the fly counts this week are already above what we consider potentially damaging to ripening berry crops, especially raspberries and blueberries. Research in Maine and other regions suggests that when 6 to 10 flies are caught in a yeast-baited trap in a week, larvae will start appearing in the fruit.

Spotted wing drosophila populations are likely to build rapidly in the coming weeks as more food (fruit) becomes available for the flies, especially if conditions remain warm and we get some rain. Now is the time to set out traps, if you haven’t already. Start protective sprays on any berries that have begun to ripen, when more than four spotted wing drosophila flies are caught in a trap, or any larvae are noticed in the fruit. Look for fruit flies hovering around fruit and symptoms of premature fruit decay.

Research has shown that dry conditions and exposure reduce the number of eggs these insects will lay in the fruit. This supports our recommendations to open up your berry plantings by pruning, especially low growth, as these insects favor dark, moist conditions, close to the ground.

Important points for managing spotted wing drosophila include:

Monitor for the flies with traps, and for the larvae in fruit.

Spray regularly and often once flies have been found in the field (every 5 to 7 days).

Harvest fruit regularly and often; do not leave any ripe/rotten fruit in the field.

Sort fruit at harvest; do not leave any soft fruit in the container to be sold.

Chill all fruit immediately after harvest to 38ºF (or as close as you can) for at least 12 hours to slow or stop development of any eggs or larvae.

Prune the planting, especially the lower region, to open up the canopy and create dry, light conditions.

Products that provide good control of drosophila on berry crops include spinosad (Radiant® for strawberries, Delegate® for raspberries and blueberries), Asana®, Brigade®, Danitol®, malathion, Exirel® (blueberries only) and Assail®. Research suggests that adding table sugar to group 4A insecticides, such as Assail®, may improve their effectiveness. The recommended rate would be 1-2 lbs. sugar per 100 gallons of spray. Also, it is recommended to add 4-16 oz Nu Film P®/100 gal with all materials to improve SWD efficacy and, if it rains after you spray, re-apply a pesticide material. (Read the label for any re-application restrictions of the same material.) Please check product labels for rates, post-harvest intervals and safety precautions.

Click here for a current list (courtesy of Mary Concklin at UConn Extension) of labeled spray materials for SWD.

Characteristics of Insecticides for Spotted Wing Drosophila Control

Trade Name

Days to Harvest
Blueberry

Days of Residual

Assail®

1

5-7

Mustang Max®

1

7

Bifenture®

1 (3 raspberry)

7

Brigade®

1 (3 raspberry)

7

Danitol®

3

7

Delegate®

3 (1 raspberry)

7

Entrust®

3 (1 raspberry)

3-5

Exirel®

3 (not for raspberry)

5-7

Imidan®

3 (not for raspberry)

5-7

Drosophila Trap, photo by David Handley

A Simple Monitoring Trap for Spotted Wing Drosophila:The trap body is made from a 16-ounce red plastic cup (we use Solo Brand P16RLR). You’ll need one that has a tight-fitting lid (we use Solo Brand 626TS). Using a 1/8” hole punch (available through art suppliers), punch about 15 holes in a row around the cup just under the lip about 1/2” apart. Leave about 2” of the diameter of the rim with no holes so that liquid can be poured in and out. Punch a second row of holes just under the first row, to give you a total of 30, 1/8” holes. Use a black permanent marker to paint a 1/2” wide black strip around the cup under the rim, right over the holes you punched. To support the trap, cut a wooden tomato stake down to about 30”. Attach a 4” or larger hose clamp near the top of the stake to act as a cup holder for the trap. (We just punched a hole in the metal band of the hose clamp and attached it to the stake with a flat-headed wood screw.) Place the trap holder in a shady, moist place in or near the fruit planting, with the cup height 12” to 18” off the ground. Fill the trap with 4 to 6 ounces of apple cider vinegar, water + sugar + yeast, or whatever bait you prefer. It is best to add a few drops of unscented soap to break the surface tension of the liquid. Place the lid on the cup to keep rain and critters from getting in, and place the trap in the holder. Adjust the hose clamp so that the trap fits in snugly but the trap holes are not covered up. Empty and re-bait the trap every week. Do not pour out the old bait on the ground near the trap, as this will draw flies away from it.

An effective commercial trap and bait is now available from Scentry. The trap is reusable and the bait lasts 4-6weeks. Cost for both is about $15 plus shipping, it is available from Great Lakes IPM Company.

For more information on identifying spotted wing drosophila (SWD) and updates on populations around the state, visit our SWD blog.

Where brand names or company names are used it is for the reader’s information. No endorsement is implied nor is any discrimination intended against other products with similar ingredients. Always consult product labels for rates, application instructions and safety precautions. Users of these products assume all associated risks.

The University of Maine is an equal opportunity/affirmative action institution.

LOW INSECT ACTIVITY CONTINUES

Storms Expected Next Week May Bring Pests into Maine

SITUATIONSome welcome rain fell on dry corn fields this week, followed by more warm weather. As a result, we are seeing rapid corn development in the fields. Early harvest has begun in some transplanted and mulched fields. Corn pest activity continues to be very low in cornfields this week, so very few fields have needed sprays. Weather predictions for the coming week indicate warm air and moisture coming up from the south, which may bring in significant numbers of corn earworm and fall armyworm.

European corn borer: There was very little borer activity in both pheromone traps and fields this week. Moths were only caught in three locations: Cape Elizabeth, Dayton and Wales. They were below threshold for silking corn at all of these sites. Feeding damage was also light, with only one field in Oxford being over the 15% spray threshold for pre-tassel to silking corn.

Corn earworm: No moths were caught in our pheromone traps this week, and therefore no sprays were recommended. There is more silking corn available for earworm moths to lay eggs on this week, so the threat is increasing. Growers should be alert for changes in the weather, such as storms moving in from southern states, that could bring more corn earworm into Maine.

Fall armyworm: No moths were caught in our pheromone traps this week, and we have not yet found any feeding damage in the cornfields we’ve scouted. We have found a few common armyworms within corn plants behaving much like fall armyworm. However, these larvae will be pupating very soon and are not likely to get into the ears. Like corn earworm, the situation for fall armyworm could change rapidly with weather coming up from the south next week.

Squash Vine Borer Larva, photo by David Handley

Japanese Beetle, photo by Edwin Remsberg, USDA

Squash vine borer moths were caught in pheromone traps in Biddeford, New Gloucester, Lewiston, Nobleboro, Farmington and Oxford this week. Only the Oxford site, which had 11 moths, was over the 5-moth spray threshold. All other sites were below the spray threshold, but we expect counts to increase state wide in the coming days. Growers with squash in southern Maine should be scouting for vine borer symptoms and protect squash plants if moths or damage are seen. See the 2018-2019New England Vegetable Management Guide for control options.

Japanese beetles are now appearing in southern and mid-state areas. These insects often find their way into cornfields and feed on the leaves, causing an interveinal skeletonizing, which is generally not significant. However, they may also feed on the silks of developing ears, causing poor tip fill. Sprays for European corn borer and/or corn earworm (except Bt’s) usually will control Japanese beetle as well.

Spotted wing drosophila: The first capture of spotted wing drosophila (SWD) occurred this week in berry fields in southern Maine. These small fruit flies can cause serious fruit losses in raspberries, blueberries and other soft fruits. This pest has already reached damaging numbers throughout much of New England, which is about 2-3 weeks ahead of what we have seen in the past few years. For more information visit our SWD blog.

Thresholds apply only to corn with exposed fresh silk. Lengthen spray intervals by one day if maximum daily temperature is less than 80°F.

European Corn Borer ThresholdsWhorl stage: 30% or more of plants scouted show injury.Pre-tassel-silk: 15% or more of plants scouted show injury.Silk: 5 or more moths caught in pheromone traps in one week.

Where brand names or company names are used, it is for the reader’s information. No endorsement is implied nor is any discrimination intended against other products with similar ingredients. Always consult product labels for rates, application instructions and safety precautions. Users of these products assume all associated risks.

The University of Maine is an equal opportunity/affirmative action institution.

LOW INSECT ACTIVITY IN CORNFIELDS

Few Moths or Damage Found This Week

SITUATIONWarm, dry weather continues to move corn development rapidly throughout the state, and many early fields are or will be silking within the next few days. Adequate irrigation is key to good ear fill during the silking stage if rainfall has been lacking. Drought stressed corn will often have very poor ear size and fill. Insect activity in cornfields was very low this week, perhaps related to cooler nighttime temperatures.

European corn borer: Very few moths were caught in pheromone traps this week, and only along the southern coast. Larval feeding damage was also below threshold in all fields scouted, as sprays applied over the past week have cleaned up fields that were recently over threshold. Some early fields are now silking, and when corn reaches that stage, sprays can be based on the number of corn borer moths caught in pheromone traps rather than feeding injury. However, none of our sites exceeded the 5 moth per week spray threshold.

Corn earworm: A single moth was caught in a pheromone trap in Lewiston this week. A spray was not recommended, even when some silking corn was present. Once more than one moth per week is captured in a silking field, a spray interval will be recommended, based on the number of moths being caught. There is still not much silking corn available for earworm moths to lay eggs on, so the threat remains low. Warmer evening temperatures and any weather fronts moving into Maine from the south could change the situation rapidly; although, as of this week, low earworm activity is also being reported from states to our south.

Fall armyworm: No moths were caught in our pheromone traps this week, and we have not yet found any feeding damage in the cornfields we’ve scouted. As with corn earworm, however, this situation could change rapidly if weather fronts from the south move into the state.

Squash vine borer moths were caught in pheromone traps in Biddeford, Lewiston and Oxford this week. Counts were below the spray threshold, but indicate that this pest will threaten squash and pumpkins this season. Moth counts in New Hampshire are over threshold this week, so activity here will rise soon. Squash vine borer moths are black and orange and resemble wasps. They lay their eggs at the base of squash plants. The larvae bore into the base of the plants, causing vines to wilt and collapse. Growers with squash in southern Maine should be on the lookout for vine borer symptoms and protect squash plants if moths or damage are seen. See the 2018-2019New England Vegetable Management Guide for control options.

Potato Leafhopper, photo by James Dill

Potato leafhopper alert: potato leafhopper is now active in vegetable and strawberry fields. These small, bullet-shaped insects feed on plant sap from the undersides of leaves, causing the leaves to become curled, stunted and yellow-streaked. Beans are often the first crop to show symptoms, but other crops are also susceptible, including potatoes and strawberries. To scout for leafhoppers, brush the leaves of the plants with your hand. The small, whitish adults can be seen flying off the plant. Look for small, light green leafhopper nymphs on the underside of injured leaves. They are about 1/16-inch long. When touched, they will crawl sideways in a crab-like manner. Control options for potato leafhoppers are listed in the New England Vegetable Management Guide.

Maine State Pomological Society Summer Tour
The event will be held on Wednesday July 18, 2018 at Dole’s Orchard, 187 Doles Ridge Road, Limington, Maine 04048. Earl and Nancy Bunting will be hosting the Maine State Pomological Society Summer Tour at their farm this summer. Much of the focus will be on the tree fruit grown at Dole’s Orchard, including apples and cherries; but there are also large plantings of pic-your-own strawberries, raspberries and blueberries. Some of the fruit is also contracted to a local brewery. There will be a morning educational program, including talks from research and Extension Specialists, followed by lunch and afternoon tours of the fields and orchards led by Earl and Nancy. Plan to come visit this beautiful farm with us! Pre-registration is requested so we know how many lunches to request. Please contact Pam St. Peter at 207.933.2100 or pamela.stpeter@maine.edu for more information.

Two pesticide applicator credits will be offered for attending the summer tour’s full day program. Registration is $15 for Maine State Pomological Society members, and $20 for nonmembers. Registration payments by cash or check will be collected at the event.

Thresholds apply only to corn with exposed fresh silk. Lengthen spray intervals by one day if maximum daily temperature is less than 80°F.

European Corn Borer ThresholdsWhorl stage: 30% or more of plants scouted show injury.Pre-tassel-silk: 15% or more of plants scouted show injury.Silk: 5 or more moths caught in pheromone traps in one week.

Where brand names or company names are used, it is for the reader’s information. No endorsement is implied nor is any discrimination intended against other products with similar ingredients. Always consult product labels for rates, application instructions and safety precautions. Users of these products assume all associated risks.

The University of Maine is an equal opportunity/affirmative action institution.

RENOVATION AND WEED MANAGEMENT ISSUE

Get Your Strawberry Beds Ready for Next Year

Manage Pests in Day-Neutral Strawberries

A mostly dry spring and warm temperatures led to a somewhat early start, but intense heat as the berries ripened significantly shortened the harvest season for many growers, and may have kept many PYO customers from coming out. A second very dry summer last year also left many beds with thinner plant populations than normal this spring, due to a lack of good runner growth. Pest pressure however, was relatively light in most fields. Spider mites and cyclamen mites were the most common problem across the state. We have seen a lot of Asiatic garden beetles flying around this summer, so growers should be on the lookout for white grub damage, especially in new plantings. (See white grub note below.) Disease pressure was also light in most fields, with leaf spot being the most common problem. A few late rain showers triggered the need for one to three fungicide treatments to keep gray mold to a minimum. Deer and turkeys did some damage to plants over the winter in several fields. All in all, the harvest was good; quantity and quality very good, with berry size down a bit, similar to last year, due to drought during flower bud formation.

Now that harvest is coming to an end, don’t forget about your strawberry plants. Renovation of your beds should begin soon after harvest to allow as much time as possible for the plants to re-establish and form lots of healthy flower buds for next year. Follow the recommended renovation steps listed below for matted row strawberries. Continue to scout for and manage disease, insect and weed problems as they arise. Some of the more common issues to be alert for during the summer are listed below.

DISEASESFoliar diseases should be monitored in your fields by regularly examining leaves. Foliar diseases are more likely to become apparent under wet weather conditions. The most common summer diseases are powdery mildew, leaf spot and leaf scorch. Fungicides available for these diseases include captan, Topsin-M®, Cabrio®, and Pristine®. See the New England Small Fruit Management Guide for detailed descriptions of these diseases and their management.

Leaf Spot, photo by David Handley

Leaf Scorch, photo by David Handley

Black root rot is a disease complex which can be brought on by a combination of factors, including nematodes, soil fungi (Rhizoctonia, Pythium), herbicide carryover, and soil compaction. Plants become weak and may wilt and die. Roots on affected plants are black and poorly developed. This tends to be a problem in fields that have been in strawberries for many seasons, and in fields that have been stressed in other ways, such as winter injury. Rotating fields to crops other than strawberries for at least three years is an important management strategy for black root rot. Improving soil drainage and breaking up hardpans in the soil may also help. Pre-plant root dips with azoxystrobin (Abound®) may also reduce incidence of black root rot.

INSECTSIf black vine weevilsor strawberry root weevils are a problem in a strawberry field that you would like to carry over, bifenthrin (Brigade®, Bifenture®) can be applied when adult feeding is noticed (usually until mid-late July). Look for notching along the leaf edges and the presence of the black or brown snout beetles. Applications should be made at night when these insects are active, and the highest rate of the insecticide should be used. For control of the grubs, a soil drench of Platinum® (thiamethoxam) insecticide should be applied during the fall and/or early spring when the grubs are active in the soil. This product has a 50-day pre-harvest interval and may also be used as a pre-plant or planting treatment for root weevils. Parasitic nematodes such as Heterorhabditis bacteriophora or Steinernema feltiae can also be applied to provide control of root weevil grubs in late August. Nematodes require specialized handling and application. Contact us or talk with one of the suppliers for more details. See the New England Small Fruit Management Guide for sources.

Black Vine Weevil, photo by David Handley

Strawberry Root Weevil Grub, photo by David Handley

White grubs have been a problem in some fields in recent years. The grubs may be the larvae of several species of scarab beetles, including June beetles, rose chafers, Japanese beetles, Asiatic garden beetles and European chafers. The beetles lay their eggs in June and July and the grubs feed on the roots of strawberries from July through mid-September. Affected plants will be stunted and wilted and may die during dry periods. Pulling up plants reveals that roots have been chewed off about an inch below the soil line. Sifting through the soil below the plants may reveal the whitish crescent-shaped grubs which can range in size from 3/8 inch to almost 1 ½ inches long, with six legs near the head and a swollen rear-end. The two most effective periods to treat plantings for grubs are in the spring prior to when they pupate (May) and in the late summer when the next generation is actively feeding (late August). Materials should be applied with plenty of water to moist soil to be sure they reach the root zone. Materials currently registered for control of grubs include Platinum® and Admire Pro®. Parasitic nematodes can also provide control of grubs and should be applied with similar timing. Nematodes are very sensitive to ultraviolet light and dehydration and must be applied with lots of water. See the New England Small Fruit Management Guide for sources of parasitic nematodes.

Strawberry rootworm (not root weevil) is a small (1/8″) dark brown to black beetle that feeds on strawberry foliage, causing it to look skeletonized. The small larvae feed on strawberry roots, further weakening the plant. Adult feeding damage on the leaves usually occurs in the spring and again in late July through August. We did find adults in many fields while we were scouting during bloom this spring. Heavy rootworm feeding weakens strawberry plants so control is warranted when injury is noticed. Sevin® is registered for control of root worm after harvest.

Strawberry Rootworm Beetle, photo by James Dill

Potato Leafhopper, photo by James Dill

Keep a lookout for potato leafhoppers; the injury has been common in new strawberry beds this year. The potato leafhopper does not overwinter in Maine, but must fly in from southern states. These small, bullet-shaped insects feed on plant sap from the undersides of leaves, causing the leaves to become curled, stunted and yellow-streaked. Symptoms are often first noticed in new strawberry plantings, and may look like herbicide damage. Leafhoppers will also infest older plantings and a variety of vegetables, flowers and fruit crops. To scout for leafhoppers, brush the leaves of the plants with your hand. The small, whitish adults can be seen flying off the plant. Examine the underside of some injured leaves. Look for small, light green leafhopper nymphs. They are about 1/16 inch long. When touched, they will crawl sideways in a crab-like manner. Controls for potato leafhoppers include Assail®, malathion, carbaryl or Provado®.

MITESTwo-spotted spider mites can increase significantly during the summer, especially in hot, dry weather. Continue to take leaf samples for spider mites throughout the summer. If more than 25% of a 60-leaf sample has mites, controls should be applied. Summer is an ideal time to use predatory mites to control pest mites, because they prefer warm temperatures, and there is less chance of an insecticide spray that might kill them. Amblyseius fallacis can provide good control of two-spotted spider mites when they are released at a rate of about 10,000 mites per acre. Predator mite releases should only be made after a spider mite infestation has been found in the field. Releasing predators into a clean field will often result in them dying, due to a lack of food. See the New England Small Fruit Management Guide for sources of predatory mites.

Two-spotted Spider Mites, photo by David Handley

Cyclamen Mite Damage on Strawberry Plant, photo by David Handley

Cyclamen mites: If your field had cyclamen mite symptoms this spring, summer is a good time to control them. After mowing off the leaves, access to the crowns where the mites reside is greatly improved. Plants showing weak growth and yellow, crinkled leaves may be infested with cyclamen mite. These mites are very small and reside down in the crown of the strawberry plant feeding on the developing leaves. They are very hard to see, even with magnification. The miticide Portal® can be effective, but must be applied with lots of water (200 gals.) to be sure that the material is carried down into the crowns.

WEEDSWeeds often become a big problem during the summer because they are forgotten among all the other demands on our time and because of limited control options. However, the importance of good weed management should not be underestimated. Keeping weeds under control this summer will help prevent future infestations. Here’s a summary of weed control options for established strawberry beds:

Cultivation: Following renovation, cultivation between strawberry rows can provide effective temporary control of annual weeds. Several types of cultivators are available which will work well in strawberry beds. Cultivators can also be used to help sweep runners into the plant rows.

DCPA (Dacthal®): A pre-emergent herbicide used in the early spring, late fall or after renovation. It offers good short-term control of some annual broadleaf weeds and grasses. It is weak on ragweed, galinsoga, smartweed, shepherd’s purse and mustard. Its action will be improved if worked into the soil by irrigation or light cultivation, and it tends to work best in lighter, warmer soils. This may be used as an alternative to terbacil or napropamide when there is a high risk of plant injury from those products.

Napropamide (Devrinol®): This pre-emergent herbicide provides good control of annual grasses, volunteer grains and some broadleaf weeds. It is typically applied just before mulching in the fall. Split applications have become popular due to the loss of other pre-emergent herbicides, e.g. half maximum rate application after renovation or in late summer after desired daughter plants have rooted, and a second half rate application once the strawberry plants are dormant. Napropamide should be activated by irrigation, rainfall or light cultivation within 24 hours of application. Repeated long-term use of this material, i.e. with no crop rotation, may eventually result in poor daughter plant establishment, due to rooting inhibition.

Terbacil (Sinbar®): An effective pre-emergent herbicide with some post-emergent activity, which should be applied at renovation time – after mowing and tilling the beds, but before new growth begins. A second application can be made in late fall, after the plants are dormant. No more than 6 oz. may be applied in a single application, and no more than 8 oz. may be applied in one season. An example of one season’s use could be 5 oz. applied at renovation and 3 oz. applied in the late fall, the latter in addition to napropamide or DCPA. Terbacil can cause injury to strawberry plants. It is important to determine appropriate rates for each location.

Clopyralid (Spur®): Has both pre-emergent and post emergent activity on many weeds. One application per crop per year following harvest to emerged weeds. Apply uniformly in a minimum of 10 gallons of water per acre. Do not tank mix with other herbicides. Offers control of clover, dandelion and thistle.

Sethoxydim (Poast®): A post-emergent herbicide for control of actively growing grasses. It will not control broadleaf weeds. It should not be applied when grasses are under stress, e.g. drought, or on unusually hot, humid days. Do not use sethoxydim within 6 weeks of terbacil (Sinbar®) applications, to avoid leaf injury. Sethoxydim should be used in combination with a crop oil concentrate. Do not tank mix with 2, 4-D. A second application is often needed for control of perennial grasses.

Clethodim (Arrow®, Prism®, Select®): A post-emergent herbicide, similar in activity to Poast®, for control of actively growing grasses. It will not control broadleaf weeds. It should not be applied when grasses are under stress, e.g. drought, or on unusually hot, humid days. Clethodim should be used in combination with a crop oil concentrate.

Paraquat (Gramoxone Inteon®): A contact herbicide for post-emergent control of most annual weeds and suppression of many perennial weeds. Paraquat will injure or kill strawberries, so applications are made between rows only, with a sprayer shielded to protect the strawberries. It should be used in combination with a nonionic surfactant. Paraquat should not be applied within 21 days of harvest or more than three times in one season.

Pelargonic Acid (Scythe®): A contact herbicide for post-emergent control of most annual weeds and suppression of many perennial weeds. Scythe® will injure or kill strawberries, so applications are made only between rows, with a sprayer shielded to protect the strawberries. This product no residual soil activity. It has a strong, unpleasant odor.

2,4-D Amine (Formula 40®, Amine 4): A post-emergent herbicide effective on most broadleaf perennial weeds. It will not control grasses, nor offer any pre-emergent control. 2,4-D should be applied immediately after harvest is complete if emerged broadleaf weeds are a problem. After application, the bed should be left undisturbed for three to five days, before mowing the leaves off the plants. This allows time for the material to be taken in by the weeds. This material can also be used when the plants are dormant (late fall or early spring) to control winter annuals and biennials. Fall applications may result in injury to the strawberries if the plants are not completely dormant. Do not tank mix 2,4-D with sethoxydim (Poast®).

Flumloxazin (Chateau®): A pre-emergent herbicide for control of broadleaf weeds, including dandelion and shepherd’s purse. For use in the fall when plants are dormant for control of weeds the following spring.

Pendimethalin (Prowl H20®, Satellite Hydrocap®): A pre-emergent herbicide that may be applied as a band with a shielded sprayer between the rows of strawberries. No weed control will be provided within the plant rows, and contact of this product on the strawberry plants will cause injury. May not be applied within 35 days of harvest. Satellite Hydrocap® may also be applied at renovation, but before new growth begins.

The use of herbicides alone rarely gives complete weed control. Some hand weeding will be necessary. To provide good weed control throughout the life of a strawberry bed, growers should concentrate on crop rotation and good pre-plant weed control.

Strawberry Bed Renovation Review

Bed renovation should begin as soon after harvest as possible. The earlier the beds get renovated, the more time runner plants have to develop, which means larger crowns and more flower buds for next year. Early renovation also improves weed management by tilling in many weeds before they go to seed, and can help with insect, mite and foliar disease control by interfering with life cycles at a critical stage of development. The first step in the bed renovation process is to determine which beds should be carried over for another year and which should be plowed down and put into a crop rotation. Beds that did not suffer much from winter injury, had good production and a good plant stand with no major weed, insect or disease problems should be carried over for another year. Beds that do not meet these criteria should be plowed down and seeded to a suitable cover crop to reduce weed, insect and disease problems that have developed, and to increase soil organic matter content. Ideally, beds that are plowed down should be rotated out of strawberries for at least three years. If properly managed, crop rotation will greatly reduce pest problems and improve the vigor and longevity of strawberry beds without the need for soil fumigation.

Renovating a strawberry bed is basically a thinning process to promote healthy new growth that can support a good crop next spring. While some parts of the following renovation scheme may be modified for individual situations, all beds should undergo the following steps once harvest is complete.

Broadleaf weed control: If perennial broadleaf weeds such as dandelion, shepherd’s purse, daisy or goldenrod are a problem and/or a high population of annual broadleaf weeds such as lambsquarters, sorrel or pigweed are present, hand-pull as many as possible, especially within the plant rows, and/or apply 2,4-D amine (Formula 40®), or clopyralid (Spur®).

Mowing Strawberry Leaves, photo by David Handley

Leaf mowing: Four to five days following the 2,4-D application (or immediately if 2,4-D was not applied) mow off the leaves of the strawberries about 1 ½ inches above the crowns. If the planting is weak, it is recommended that this step of the renovation process be skipped.

Fertilization: Apply 40 to 60 pounds of actual nitrogen per acre (use the higher rate on sandy soils and fields where growth has been weak). Phosphorus and potassium applications should be made according to soil test recommendations. Soil testing kits and information are available from your county Cooperative Extension office.

Plant thinning: For the single matted row system, strawberry plant rows should not be any wider than 24 inches. After mowing off the leaves, till the sides of the rows to narrow the beds back to a width of 12 to 18 inches. Use the wider setting for varieties that tend to throw few runners or any fields experiencing drought stress. Set the tiller so that it incorporates the mowed leaves and spreads about one inch of soil over the remaining crowns at the same time. This will reduce leaf disease and mite problems, and help stimulate new root growth on the remaining plants.

Pre-emergent weed control: To control annual weeds, apply terbacil (Sinbar® 80WP) according to label directions (2 to 6 oz. per acre). Be sure to follow all label precautions. To avoid plant injury, do not use terbacil if you do not intend to mow off the leaves. Napropamide (Devrinol®) or DCPA (Dacthal®) may be used as an alternative to terbacil at this time, as described below. If you are not using herbicides, regular cultivation, before weeds are more than 2” tall, will be needed throughout the summer.

Strawberry Irrigation, photo by David Handley

Subsoiling: Soil compaction caused by tractor and picker traffic in the field can cause soil drainage problems and interfere with good root development. Using a subsoiling blade between the rows will break up compacted layers of soil and improve water infiltration. Subsoiling is best done late in the renovation sequence to prevent interference from straw and crop residues.

Irrigation: To encourage rapid plant growth and get the most out of fertilizers and herbicides, irrigate the beds regularly. Strawberries will grow best if they receive 1 ½ inches of water per week during the growing season.

Don’t forget your plants once these renovation steps are completed. Check the strawberry fields regularly during the summer for pest problems. Finding and managing problems early can prevent major problems next spring. Pay close attention to the following items.

NUTRITIONFollowing the application of 40 to 60 pounds of actual nitrogen at renovation, another 20 pounds of nitrogen should be applied in mid- to late-August to stimulate flower bud development. One way to determine the nutrient status of strawberry plants during the summer is to have a leaf tissue analysis done. Tissue analysis offers a view of what is happening within the plant, and can spot any nutrient deficiencies. In combination with regular soil tests, tissue analysis will provide a complete picture of a field’s fertilizer needs. For more information about tissue analysis contact the Analytical Lab and Maine Soil Testing Service, 5722 Deering Hall, Rm. 407, University of Maine, Orono, Maine 04469-5722, telephone: 207.581.2945.

Pest Management for Day-Neutral Strawberries

Most of the important pests that damage June-bearing varieties can be as much or more of a problem on day-neutral types. Because day-neutral strawberries will have buds, flowers and fruit all occurring at the same time, it is critical to pay close attention to the required number of days to harvest after a pesticide application, to be sure you can safely harvest ripe fruit while still protecting buds and blossoms. Some of the more important pests are listed below, along with currently recommended pesticides and days to harvest as stated on current labels.

Spotted wing drosophila (Drosophila suzukii) is a concern for day-neutral strawberries, fall raspberries and blueberries. This is a small fruit fly, similar to those that hover around the bananas in your kitchen. However, this species will lay its eggs on fruit before it ripens, resulting in fruit that is contaminated with small white maggots just as it is ready to pick. Infested fruit quickly rots and has no shelf life. This insect can complete a generation in under two weeks, with each adult female laying hundreds of eggs. Therefore, millions of flies can be present soon after the introduction of just a few into a field. Frequently repeated insecticide sprays (1 to 2 per week) may be needed to prevent infestations once the insect is present in a field. Spotted winged drosophila can successfully overwinter here, although it may not build up to damaging levels until late in the summer. Products that provide good control of drosophila on strawberries include Radiant®, Brigade®, Danitol®, malathion and Assail®. Keeping fields clean of over-ripe and rotten fruit will also help reduce the incidence of this insect. For more information on identifying spotted wing drosophila and updates on populations around the state, visit our Spotted Wing Drosophila blog.

Tarnished plant bug: This is one of the most prevalent and persistent pests of day-neutral strawberries, because summer flowering coincides with peak populations of this insect. Adult and nymph stages feed on the flowers and developing fruit, causing them to have seedy ends and other malformations. Regular insecticide applications are often required to keep the damage in check. Scout the flower clusters for adults and nymphs often to determine if controls are necessary. Insecticide products for tarnished plant bug include:

Tarnished Plant Bug on Strawberry Flower, photo by David Handley

Tarnished Plant Bug:

Product

Days to Harvest

Brigade®

0

Pyganic®

0

Assail®

1

Dibrom®

1

Rimon®

1

Malathion

3

Two-spotted spider mites: Mites can become a problem during the summer when the growing conditions are warm and dry. In addition to infesting the leaves, mites can move onto the fruit, reducing marketability. Plants that are drought-stressed, over fertilized with nitrogen, or prone to dust covering, e.g. growing beside a dirt road, are especially prone to mite infestation. Predatory mites can be an effective means to control spider mites and keep them in check over the season. Releases should only be made when spider mites are present in the field to provide the predators with a source of food. Most of the products labeled for controlling spider mites will also kill predatory mites; so, do not use these products after predators have been released. Scout for mites often during the season by examining the undersides of the leaves. Control is warranted if more the 25% of leaves examined have mites.

Two-spotted Spider Mites, photo by David Handley

Two-Spotted Spider Mites

Product

Days to Harvest

Brigade®

0

Zeal®

1

Vendex®

1

Acramite®

1

Danitol®

2

Agri-Mek®

2

Oberon®

3

Savey®

3

Kelthane®

3

Potato leafhoppers, sap beetles, thrips and spittlebugs may also become problems on day-neutral strawberries, but are less frequently observed than tarnished plant bug and spider mites. Recommendations for these insects can be found in the current edition of the New England Small Fruit Management Guide.

Foliar and fruit diseases also need to be managed on day-neutral strawberries, and should be controlled in much the same way as they are for June-bearing varieties. Most of the fungicide products labeled to control gray mold, powdery mildew, leaf spot and leaf scorch have either zero or one day to harvest, so protecting blossoms at the same time as fruit is near harvest should not be a problem; but be sure to check labels carefully and schedule your sprays and harvests accordingly. Anthracnose fruit rot can be especially troublesome for day-neutral strawberries, because it grows well under warm conditions and spreads by splashing water, which is encouraged on plastic mulch. Fungicides registered for control of anthracnose include Cabrio®, Abound®, Pristine® and Switch®, all of which have zero days to harvest restriction.

Strawberry Production WorkshopA strawberry workshop will be offered on Thursday January 17, 2019 at the Augusta Civic Center, concurrent with the Maine Agricultural Trades Show, January 15-17, 2019. Details and registration will be available this fall.

Where brand names are used, it is for the reader’s information. No endorsement is implied nor is any discrimination intended against products with similar ingredients. Always consult product label for rates, application instructions and safety precautions. Users of these products assume all associated risks.

The University of Maine is an equal opportunity/affirmative action institution.